Extant research on vocabulary development in pre-school children focuses on understanding the breadth and depth of the growing lexicon. The vocabulary system, however, comprises the lexicalization of concepts, and also the broader system of connections between words and concepts. The next step in understanding the earliest stages of vocabulary growth is to investigate these connections, as this process is central to understanding how children construct meaning and organize the world around them. For example, when and how do children learn that cat and dog are related? Similarly, how do Spanish-English bilinguals learn that cat and gato refer to the same concept? Such questions have spurred debate in the field of psycholinguistics about the representation of multiple languages in the adult brain. However, to understand how flexible systems emerge, we must investigate these questions from a developmental perspective (Francis, 2005). The recent use of direct response measures in children within the second year of life allows us to explore lexical networks at the earliest stages of emergence by using infants' prompted looking times and touch responses (Arias-Trejo & Plunkett, 2009; Singh, 2013; Poulin-Dubois et al, 2012). Understanding semantic development and its relation to language experience will answer important questions about language and concept representation in development. Further, the proposed research will help to clarify the relationship between language experience and cognition, as we investigate single and dual language learning and its effects on conceptual development in two understudied populations. In particular, Spanish monolinguals and bilinguals make up a significant and rapidly growing proportion of children in the U.S. Despite this, they have been the focus of relatively little research on early lexical development. Indeed, the NICHD has taken a recent focus on understanding health disparities in the US. Consistent with this focus, it is important to extend investigations of early language to children across linguistic communities. The proposed research plan will evaluate lexico-semantic development in Spanish monolingual and Spanish-English bilingual infants within the second year of life by examining responses using a Preferential Looking Paradigm, as well as an adaptation of the Computerized Comprehension Task (Friend & Keplinger, 2008; Friend, Schmitt, & Simpson, 2012). Specifically, the proposed research plan will directly compare lexico-semantic priming in monolingual and bilingual infants. By comparing visual and haptic response modalities, the research will assess the strength of lexico-semantic connections within and across languages, and how factors such as SES, language dominance, proficiency, and age influence lexical organization. Evaluating differences in early lexical development informs our understanding of preparedness for literacy, as oral language skills are the cornerstone of later reading skills. By examining early oral language acquisition, we can inform reading intervention and teaching strategies that are sensitive to English and Spanish speakers alike.